Spontaneous Combustion Explained

When you hear about spontaneous combustion, the mind most likely first goes to the crazy stories about the man who burned to death in his chair, but his surroundings remained unaffected by the fire. This is called spontaneous human combustion, and there are some instances where certain variables were just right, and no other explanation could be made, but for the sake of chemistry and facts, we will be discussing self-heating oils and other materials that can in fact lead to a spontaneous explosion!

A person is changing the oil in their car, or cleaning up some oily mess on their garage floor, and doesn’t think twice about tossing the used rags into the garbage, since those rags are most likely unusable from that point on. Minutes, sometimes hours go by, and then suddenly, a fire breaks out, and the victim has no idea why the fire started. The resident wasn’t even at home when the fire was started. Upon inspection by trained individuals, the investigators discover portions of towels, and soon realize the garbage can with the oily rags is the origin and cause of the fire. The investigator determines the cause of the fire is spontaneous combustion.

Spontaneous combustion is described by the National Fire Protection Agency (NFPA) as a byproduct of spontaneous heating. This phenomena occurs when a material increases in temperature without drawing heat from its surroundings, an open flame for example. In this instance, the material was the vapors from the oils on the rags mixed with oxygen that caused a chemical reaction called oxidation. Once the material reaches its ignition temperature, spontaneous combustion or ignition occurs. So the name spontaneous combustion is a bit misleading because the fire doesn’t erupt out of nowhere. Three elements are required: fuel, oxygen, and a source of heat. When we think of a source of heat, we think flames, but with spontaneous combustion, there is no flaming ignition. The reason the pile of oily rags ignite is because there is no way to dissipate the heat from the chemical reaction. If the rags had not been in a pile, no reaction would occur. There are many other common household materials that are prone to spontaneous combustion. They include, but not limited to: linseed oil, coal, hay, and other agricultural products to name a few. The most recorded and confirmed causes of spontaneous combustion cases were from improper disposal of oily rags (Evarts 2011).

Avoiding spontaneous combustion is fairly simple. If you use rags to clean an oily mess, be sure to hang them separately outdoors on a clothesline to dry, or indoors away from furnaces and other heat sources. Make sure that your coal is stored in a dry place, away from exposure to moisture. Store hay in cooler, dark areas and monitor the temperature. There is heat-resistant bacteria in hay that once it reaches about 150 degrees, it starts a chemical reaction, which in turn rapidly increases the temperature until it ignites. The same goes for decomposable materials like mulch or compost. When you pile it on top of each other, the heat gets trapped, temperature goes up, and you have ignition.

Because spontaneous combustion isn’t normally the suspected source in a fire case, the investigator will want to take several samples from different areas of the fire debris to send in for analysis to prove or disprove the theory. At Armstrong Forensic Laboratory, we test for identification of ignitable liquids, vegetable oils residue, soot damage, and identification of the unknown. Call us at 800-644-4175 or 817-275-2691 DFW area for information on how Armstrong Forensic Laboratory can assist with your next fire investigation, or simply fill out the ‘Ask An Expert’ form on our website for a free quote!

Below are some links about spontaneous combustion cases and other sources of facts used in this article: